Remotely powered electronic devices and related systems are known. For example, U.S. Pat. No. 5,099,227, issued to Geiszler et al. and entitled “Proximity Detecting Apparatus,” discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source, then uses both electromagnetic and electrostatic coupling to transmit stored data to a receiver, often collocated with the remote source. Such remotely powered communication devices are commonly known as radio frequency identification (“RFID”) tags.
RFID tags and associated systems have numerous applications. For example, RFID tags are frequently used for personal identification in automated gate sentry applications, protecting secured buildings or areas. These tags often take the form of access control cards. Information stored on the RFID tag identifies the tag holder seeking access to the secured building or area. Older automated gate sentry applications generally require the person accessing the building to insert or swipe their identification card or tag into or through a reader for the system to read the information from the card or tag. Newer RFID tag systems allow the tag to be read at a short distance using radio frequency data transmission technology, thereby eliminating the need to insert or swipe an identification tag into or through a reader. Most typically, the user simply holds or places the tag near a base station, which is coupled to a security system securing the building or area. The base station transmits a signal to the tag that powers circuitry contained on the tag. The circuitry, in response to the signal, communicates stored information from the tag to the base station, which receives and decodes the information. The information is then processed by the security system to determine if access is allowed or appropriate. Also, RFID tags may be written (e.g., programmed) and/or deactivated remotely by an excitation signal, appropriately modulated in a predetermined manner.
Some conventional RFID tags and systems use primarily electromagnetic coupling to remotely power the remote device and couple the remote device with a reader (e.g., an emitter system and a receiver system). The reader (e.g., the emitter system) generates an electromagnetic excitation signal that powers up the device and causes the device to absorb, re-radiate or backscatter a signal which may include stored information. A receiver on the reader receives the signal produced by the remote device.
Traditional RFID manufacturing processes generally require a direct die attach to either a 3-layer antenna or to a strap that is then attached to a single layer antenna. The direct die attach process, an example of which is shown in FIGS. 1A-1B, is a relatively slow process, which can make it relatively expensive for a given throughput. The size of the die is limited, and the relatively small die dimensions result in a need for higher accuracy pick and place systems, which further increases costs.
Referring to FIG. 1A, conventional RFID tags are formed by a process that includes dicing a wafer manufactured by conventional wafer-based processes into a plurality of die. A die is then placed onto an antenna or inductor carrier (which may contain an antenna, inductor coil or other conducting feature) in a chip-to-antenna attach process. Alternately, the die can be attached to an intermediate carrier (or strap) in a two-step chip-to-strap/strap-to-antenna attach process.
In the two-step process, a die 120 is attached to a strap (or carrier) 140. Electrical paths 130 and 132 from the die 120 to relatively larger and/or more widely distributed areas (e.g., 134 or 136) for attaching ends of the antenna are present in certain locations on the strap 140. This assembly may then be attached as shown in FIG. 1B to a support film 150 containing inductor/antenna 152. Because the pads 134 and 136 (together with the paths 130 and 132 and the die 120) connect the ends of the antenna 152, the assembly on the strap 140 is sometimes known as a “strap.” This attach process may include various physical bonding techniques, such as gluing, as well as establishing electrical interconnection(s) via wire bonding, anisotropic conductive epoxy bonding, ultrasonics, bump-bonding or flip-chip approaches. Also, the attach process often involves the use of heat, time, and/or UV exposure. Since the die 120 is usually made as small as possible (<1 mm2) to reduce the cost per die, the pad elements for external electrical connections to the die 120 may be relatively small. This means that the placing operation should be of relatively high accuracy for high speed mechanical operation (e.g., placement to within 50 microns of a predetermined position is often required).
Manufacturing conventional RFID devices using the strap attach process also has cost limitations because the process inherently requires the same die attach process as the direct die-to-antenna attach process to place the die on the strap. The strap attach process also introduces additional process steps, which result in lower yields and higher costs.
Some RFID manufacturing processes use a printed integrated circuit (PIC). The printed integrated circuit is generally larger than a photolithographically-produced die on a single-crystal substrate (e.g., a silicon wafer). The relatively large size of the printed integrated circuit (e.g., >1 mm2) enables direct die attachment to (or placement on) a single layer antenna. An example of this process is shown in FIGS. 2A-2B (see, e.g., U.S. Pat. No. 7,152,804). The cost of direct die attachment of large printed integrated circuits is generally lower than traditional pick-and-place die attachment. However, the cost of certain adhesives and/or of crimping or welding processes may still be higher than desired.
FIG. 2A shows tag precursor 200, comprising strap or interposer 232, having thereon pads 234 and 236 and integrated circuitry 210. Generally, integrated circuitry 210 is formed on a first major surface of strap 232. The integrated circuitry 210 can be realized as a printed inorganic circuit, largely using the techniques described in U.S. patent application Ser. Nos. 10/885,283 and 11/104,375, filed on Jul. 6, 2004 and Apr. 11, 2005, respectively, the relevant portions of which are incorporated herein by reference. Holes or vias (not shown in the Figures) may be formed in the major surface of substrate 232 opposite that on which pads 234 and 236 and integrated circuitry 210 have been formed, if backside attachment to the antenna is to be performed.
FIG. 2B shows an antenna and/or inductor carrier 250, comprising carrier 250 and an antenna and/or inductor 252 thereon. Generally, the antenna and/or inductor 252 are formed on a first major surface of carrier 250. The antenna and/or inductor 252 can be realized as an etched structure on a dielectric substrate, a plated structure, or a printed structure. As shown in FIG. 2B, the strap/interposer 232 can be attached to the carrier 250 containing the inductor/antenna 252 such that electrical connections are formed between pads 234 and 236 and terminals of antenna/inductor 252 at locations corresponding to the holes or vias (not shown) in substrate 232. Alternatively, the carrier/strap 232 and the carrier 250 can be attached face-to-face, such that direct electrical connections are made between the pads 234 and 236 and terminals of antenna/inductor 252. This carrier-based process may have advantages for flip-chip or bump bonding approaches, where the small pad dimensions and relatively small pitch between adjacent pads may make it more expensive or disadvantageous to implement bumps, balls and/or other interconnect elements onto the integrated circuit, the pads 234 and 236, and/or the inductor/carrier substrate 250 by conventional means.
Conventional RFID manufacturing processes generally use either a relatively complex chip-to-antenna attach process (not shown in the Figures) or a two-step chip-to-strap/strap-to-antenna attach process, as shown in FIGS. 1A-1B. Either process requires high-precision pick-and-place equipment for the chip attach. The high precision pick-and-place equipment has a relatively high capital cost and is typically slower than lower precision equipment. Also, the process of picking out a separated (sawn) die 120 (FIG. 1A), moving it to the strap 140 to which it is to be bonded, accurately placing it in its appropriate location, and making the physical and electrical interconnections can be a relatively slow process. As a result, the conventional attach process has a proportionately high cost relative to the overall manufacturing cost.
In the case of a process that uses a strap or interposer (e.g., strap 232 in FIG. 2B), cost and throughput advantages are achieved by first forming the integrated circuit 210 on a continuous or discrete process sheet, and individual carriers/straps 232 are formed therefrom by singulation. Relatively large and more widely distributed pads 234, 236 can be formed in other locations on the carrier 232 to allow high-throughput, low resolution attachment operations such as crimping or conductive adhesive attach to the substrate 250 and antenna 252. Electrical paths from the integrated circuit 210 to the pads 234, 236 can be formed simultaneously with the pads 234, 236.
The price of tags is a significant focus within the RFID industry. High RFID tag prices have been an obstacle against widespread adoption of RFID technology, especially in item-level retail applications and other low-cost, high-volume applications. One way of reducing wireless device (e.g., RFID tag) costs is to develop a tag structure and process that incorporates (and preferably integrates) a less expensive substrate, simplifies or eliminates any attach processes, a stable and effective antenna, and printed front end devices and logic circuitry.